This project is concerned with two aspects of gene expression: (i) selectivity of transcription and (ii) post-transcriptional processing of RNA. Both phenomena involve specific interaction of proteins with nucleic acids and the investigation will be aimed at understanding the mechanisms of this interaction and their relevance to physiological control events. Bacteriophage T4 development in E.coli provides a useful model system open to a combination of genetic, biochemical and physiological approaches. In T4 development, different groups of genes are turned on and off by means of virus-induced modification of the host transcription machinery. Previously we have shown that T4-induced ADP-ribosylation of RNA polymerase alfa-subunit turns off certain T4 promoters in vitro. The mechanism and biological role of this phenomenon will be studied. Previously we have mapped several transcription termination sites in the T4 tRNA gene region. The interaction of RNA polymerase with these sites will be analyzed in order to understand the fine mechanism of transcription termination. We also intend to develop an in vitro system allowing to use the termination sites for the analysis of T4-induced antitermination (anti-rho) effect: the presumed mechanism of switching the T4 gene expression from immediate-early to delayed-early functions. Purified primary in vitro transcripts of T4 DNA provide convenient substrates for the search and study of RNA processing enzymes. In the previous work, a new endonuclease involved in maturation of transfer RNA was partially purified. We intend to further purify and study this enzyme which is thought to be a major tRNA processing endonuclease of E. coli. It is also proposed to continue our studies of the involvement of Ribonuclease III in the processing of T4 mRNA.